How valuable can people with mental disabilities be to others? In this article I present ethnographic material on L’Arche, a Christian charity that provides care. I describe how carers there are trained to see cognitive disability as producing not simply an absence of rational agency, but also the presence of a quite different way of actively inhabiting the world. I argue that, by learning to recognize and value this unusual kind of agency, carers in L’Arche subvert the terms of a recent philosophical debate about the worth of people with cognitive disabilities. They demonstrate that people can value others not just as rational moral subjects, or simply as passive objects of care, but also as charismatic and intuitive agents who actively depart from standard norms of personhood.